Method and apparatus for seismic surveying



April 7, 1942.

J. L. ADLER METHOD AND APPARATUS FOR SEISMIC SURVEYING F11 d Aug. 15, 1940 'Patented Apr. 7, 1942 UNITED @STATES PATENT OFFICE METHOD AND APPARATUS Fon sErsMIc suBvErnvG Joseph L.' Adler, Houston, Tex., assigner to Fabian M. Kannenstine, Houston, Tex.

Application August 13, 1940, serial No. 352,419 s claims. (c1. rs1-n.5)

Aduced of the waves arriving at each of such points. In order to produce a record of the arriving waves a transducer or geophone; used singly or in groups, is utilized to convert the' seismic impulses into electrical impulses, the latter of which are transmitted thru lters so that only the energy of a predetermined band of frequenciesv actuates the recording instruments.

Geological strata diier in their capabilities of reecting seismic impulses of different frequencies. The present invention makes use of this fact by utilizing different bands of frequencies for producing the various wave traces and by means'of such technique it is possible to obtain information in addition to that which 1s obtained in conventional practice. This is accomplished by utilizing diiIerent band pass filters in the various recording channels, vsuch filters being so constructed and arranged that multiple wave traces represent energy from all portions of the frequency spectrum of the seismic impulses.

A primary object of the invention is to provide novel method and apparatus for obtaining frequency analyzed seismic records which reveal a an indication of the predominating or character- Y istic frequency of each individual stratum.

Still another object is to provide with a single instrument and one operation records at a plurality of frequencies from a single source of seismic impulses.

The foregoing objects together with other objects will be apparent from the following description taken in connection with theY accompanying drawing, in which:

Fig. 1 is a diagrammatic illustration of a field setup used in practicing the invention;

Fig. 2 is a reproduction of a graphical record obtained in accordance with the invention.

In the arrangement shown in Fig. l strata. l and 2 exist beneath the overburden 3 extending downwardlyfrom the earth surface I. In order to obtain information as to the nature and location of the strata I and 2, a shot hole is drilled in the earth at 5 and a charge of explosive E is detonated therein so that seismic waves are set up in the earth :and travel in all directions from the center of disturbance.

maximum of information relative to the subsurface geological strata.

Another object is to provide a record of a seismic event by utilizing a wide range of frequencies present in the seismic impulses. f

Still another object is to obtain desired seismic'f 1 of wave` traces of av seismic event, each individual trace being produced by a predetermined `band of frequencies and allw of such bands 'covering the frequency spectruni'of they seismic impulses.l

A further object is toobtain in seismic records A plurality of geophones indicated as l0 to I'l are positioned in relative spaced position from each other and the shot hole 5 and are in contact l with the earth so that the waves directed aloner thepaths 20 and 2l are reflected from the strata I and 2 along the lines 22 and 23 to the respective geophones. It is to be understood that, while an individual geophone is illustrated for each recording channel, a plurality of rgeopllones may be used for each or all of the channels in a manner well known'in the art.' It is also to be noted plifier 26. The outputs of these ampliers are turn transmittedxto filters 30 to 3'linclusive, of

which one is provided for each recording channel,

These lters are of well known construction and each is designed to pass a band of frequencies as for example, a band having a width of twenty cycles. In the illustrated arrangement whereby the graphical rcord of Fig. 2 is produced the median frequencies of the bands of frequencies passed by the lters 3D to 31 inclusive are 15, 20, 25, 30, 40, 50, and 80. Itis to be noted that i these bands of frequencies increase slightly in width asthe higher frequencies are approached.

The arrangement is therefore such that substantially all frequencies in thespectrum of the seiscompleted record as already indicated is shown at Fig. 2 in which the wave traces All to 41 are respectively recorded by the energy passed thru the respective filters 30 to- 31. The abscissae of these curves represents time, the graphical record beingseparated into intervals of one-thousandths of a second.

The shot point is indicated 'by trie break in curve .0 at the point B. The initial recording in the respective'channels shown at 5I indicates the arrival of Vthe directly transmitted waves set up the initiatingI impulse. 'Thereafter it is to be noted that certain vibrations are shown at 52, 53 and 54 due to'seismic unrest and such portions of the curve are of little orno significance. At 55, however, is fshown the arrival of the reflected waves from the stratum l and it is to be noted that this stratum is of such nature that the predominant portion of the record lies within the higher recorded frequencies. After the arrival of the reected waves from the stratum l a short interval of time'elapses before the.,arrival of theV reflected waves from the stratum 2. The record of these latter waves is indicatedl at 56 and it willv be noted that the predominant portion of th'e recording energy is in the vicinity of thirtyl cycles per second.

From the foregoing it is believed apparent that' the record illustrated in Fig. Zand obtained in accordance with the invention vprovides an indiy v cation as to the location ofthe strata and 2 and also the nature .of suchstrata since the record is frequency analyzed thereby providing information regarding 'the frequency reflection charac,- teristics o f the respective strata. Attentionis also directed to the fact that the method of the invention is of particular importance where the strata. l and 2, or additional strata at greater or lesser depth, are in relatively close proximity to each other.

cessive refiections can beV readily separated, whereas they would appear as superposed and obscured traces if frequency analysis in accordance with the invention were not utilized.

While the foregoing specic 4disclosure of thev Such condition willl bring the traces 55 and 56 in closer relation because of the shorter in- A A terval of time betweenlthe arrival of reflections from successive beds. In such` event the sucapparatus and technique of the invention refers to the production 'of a single wave trace in each geophone circuit it is to be understoodvthat the energy from any or all of the individual geophones 5 may be utilized to produce a plurality of wave traces each of which is produced by a selected band of frequencies from the seismic spectrum. The disclosure is offered as illustrative only and it is inten'ded that the in ,vention shall not be conl0 fined thereto but shall broadly comprise method and apparatus for obtaining in a seismic record the maximum of information relative to the location and nature of subsurface strata by the provision of a frequency analyzed record of the Waves reflected from such strata.

What is claimed is:

l. In the seismic method of geophysical prospecting wherein a plurality of spaced detectors convert arriving seismic impulses into pulsations of electrical energy to obtain frequency analyzed seismic records, the steps of transmitting-the pulsations from each point of detection to an amplifier, coordinating a series of band pass filters, conducting the amplified impulses through such series of band pass filters, the band of frequencies passed by each individual filter being different from that passed by each of the other filters so that the series of filters when coordinated together pass the spectrum of fre- .quencies present in the arriving seismic impulses,

and recording in separate 'traces the impulses passed by the respective filters.

2. In 'the seismic method of geophysical prospecting wherein seismic impulses arriving at a plurality of predetermined spaced points are detected and recorded, the stepsof sending up a series of coordinated filters eachof which is to filter a predetermined band of frequencies, 'filtering the detected impulses fromeach point to pass `40 only a limited band of frequencies from such point,l the frequencies passed from all of the points /comprising a` plurality of frequencies greater than those covered by any individual band of the frequencies in the spectrum of the seismic impulses, and recordingas an independent trace the impulses passed from each of the points of detection.

3. In the seismicv method of geophysical prospecting wherein the seismic impulses arriving ata plurality of spacedV points are independently detected andI recorded, the steps of` filtering from the detected impulses from each point all except a limited band of frequencies, the series of bands of frequencies being coordinated so that the different bands of frequencies passed from the points of detection include energy from all portions of the spectrum of the seismic impulses, amplifying the energy-in the respective bands of frequencies, and recording as an independent traceA the amplio fied impulses from each of the bands; i

JosEPI-IL.. ADLER 

